The present invention relates to nebulizer devices, and in particular to nebulizer devices used in medical applications.
Nebulizers are used in medical environments to humidify the air supplied to a patient. Heretofore a wide variety of nebulizer designs have been developed and have been used with a variety of patient ventilating systems. In a typical system a nebulizer is coupled to a flowmeter which is in turn coupled to an oxygen source, such as an oxygen tank or hospital oxygen supply system. The flowmeter is used to adjust the oxygen flow rate supplied to the nebulizer. The nebulizer normally includes some type of nozzle that provides an air jet adjacent a fluid supply, which typically consists of a capillary tube that leads to a fluid supply bottle. The oxygen jet induces liquid flow up the capillary tube to the jet where the fluid is entrained as a fine aerosol mist. The humidified oxygen is then passed through tubing to some type of respiratory device, such as a respirator mask, endotracheal tube, oxygen tent or the like.
In the past nebulizers have also been used to regulate the oxygen concentration of the gas supplied to the patient, referred to as the "fraction of inspired oxygen" (FIO.sub.2). For this purpose nebulizers typically have some type of valving system that allows atmospheric gas to vent into the oxygen flow at the nozzle region. The oxygen jet is used to entrain and mix with the atmospheric gases. Adjustment of the valving mechanism therefore regulates the atmosphere to oxygen ratio that is forced through the nebulizer device to the patient. However, since the oxygen flow through the nebulizer is used to induce a vacuum that draws atmosphere into the nozzle region as well as draws fluid up the capillary tube and into the oxygen stream, the size of the vent mechanism opening is limited. If an excessive atmospheric opening is provided, the fluid entraining oxygen will simply exhaust out through the vent mechanism rather than being directed toward the patient.
One substantial problem associated with previous nebulizers is the restriction of air flow to the patient. In instances in which the patient requires a low fraction of inspired oxygen, a relatively large amount of atmospheric gases may be drawn in through the nebulizer and supplied to the patient. In such an application the venting mechanism is fully opened, resulting in a high flow rate to the patient and a low fraction of inspired oxygen or oxygen percentage. In other instances, however, the patient may require a high fraction of inspired oxygen. In these applications the vent mechanism must be substantially closed, reducing the amount of atmospheric gases which are supplied to the patient and thus dramatically reducing the overall gas flow to the patient. Nonetheless the patient normally still requires a relatively high overall flow rate for respiration. In such instances one solution is to provide two nebulizer systems in order to double the flow rate to the patient yet maintain the appropriate fraction of inspired oxygen. Alternatively, the respiratory tubing downstream of the nebulizer may have an additional oxygen tube leading from another flowmeter which bleeds in oxygen to the previously humidified gas mixture. Although this permits the fraction of inspired oxygen to be increased, the atmosphere venting mechanism must be adjusted to accommodate this increased oxygen content and the nebulizer is not calibrated for this supplemented flow rate, so that this varying of the flow rate renders inaccurate the regulation of fraction of inspired oxygen. Inconsistent oxygen and flow delivered to the patient may result.
In another attempt to solve these problems, an additional valve has been placed on the nebulizer nozzle, which when opened permits additional oxygen to pass through another port on the nebulizer nozzle. This structure suffered from a similar problem as the flowmeter-nebulizer sequence noted above, in that the atmosphere venting mechanism is calibrated and accurate only as to a given flow rate of oxygen through the nebulizer. Changing this flow rate renders inaccurate the atmosphere venting mechanism and is a potential hazard.
In the above systems, inaccurate oxygen concentrations as a result of varying the flow rate can be potentially dangerous to the patient. The common practice of connecting a flowmeter and nebulizer poses such a potential hazard. Even in situations that do not pose a potential hazard to the patient, such multiple adjustments are confusing and difficult to estimate. Multiple systems require duplication of equipment which increases the expense of administering this type of therapy.